The poor prognosis of patients with pancreatic adenosquamous carcinoma may impact on the decision to consider second line chemotherapy. In the case described, despite early relapse during adjuvant gemcitabine therapy, the patient proceeded to have a 34.6 month remission on second line capecitabine. This is an exceptional response. To our knowledge, this is the first documented case of a patient with adenosquamous cancer having an exceptional response to second line treatment, in the context of early disease relapse.
CDA mediates the inactivation of gemcitabine [
9] and, conversely, the activation of capecitabine [
10]. Relative to the normal pancreas, it has been reported that CDA is overexpressed in pancreatic cancer [
11]. Both circulating CDA activity [
12,
13], and intra-tumoural expression of CDA [
8,
14,
15], varies between patients and may impact on the response of patients to gemcitabine and / or capecitabine therapy. Whereas low circulating CDA activity has been associated with a better response to gemcitabine treatment in patients with pancreatic cancer in two studies [
12,
13], this was not the case in a subsequent multicentre prospective trial with 120 patients treated with gemcitabine [
16]. For intra-tumoural CDA expression, preclinical data have identified strong expression to be associated with reduced response to gemcitabine [
14] and increased response to capecitabine [
15]. Clinical data investigating the impact of intra-tumoural CDA activity are lacking, although data from a recent study of 105 patients with pancreatic cancer do suggest that intra-tumoural CDA expression may be predictive of response to sequential, but not concomitant, therapy with nab-paclitaxel and gemcitabine in the first line setting [
8]. Germline CDA single nucleotide polymorphisms have also been associated with CDA activity and / or toxicity or survival with gemcitabine based therapy [
17‐
19]. However, CDA single nucleotide polymorphisms are detected in only a subset of patients with reduced CDA activity, supportive of other regulatory mechanisms determining CDA expression and activity (reviewed in [
20]). In this case report, we identify strong intra-tumoural expression of CDA as a potential contributor to the patient’s disparate responses to these two chemotherapeutic agents. Importantly, whole blood CDA activity was not elevated, indicating that increased CDA activity was not systemic, and capecitabine was well tolerated. Similar consideration, and reporting, of how intra-tumoural drug metabolism may impact on responses to chemotherapy will facilitate our understanding of these responses and our treatment decisions in the future.
The choice of adjuvant chemotherapy for pancreatic adenosquamous cancer has, to date, been largely guided by trials conducted almost exclusively in patients with pancreatic adenocarcinoma [
21‐
24]. Data from the ESPAC-4 trial suggest that combination therapy with gemcitabine and capecitabine may offer further survival benefit over single agent [
23]. Conversely, retrospective analyses restricted to pancreatic adenosquamous cancer have suggested that this subgroup may be most responsive to combination therapy with platinum agents [
3,
4]. Whilst evidence supporting the optimal adjuvant regimen for pancreatic adenosquamous tumors remains limited by the relatively low incidence of the disease, this case report demonstrates that early relapse on one regimen may be compatible with a subsequent exceptional response to second line chemotherapy, particularly when a biochemical rationale exists for the failure of initial chemotherapy.